I think if Valve chose to promote this and it wasn't automatically placed on the front page due to a surge in popularity, it's probably because Valve is trying to show itself to be a marketplace where no idea is censored, no matter how unpopular and that their competitors have asinine policies.

Look at the whole Hatred debacle. Some people think it's the most offensive game of all time and should be banned, but Gabe himself came out and said that that's no reason to pull the game.

Besides, when it comes to censorship in games, it's usually from gross misunderstandings or willful ignorance. Banning all Civil War themed games because they display a flag in a historical context is a good example. The game is in no way promoting the ideology behind the flag.